There is growing evidence that tumors contain a subset of cells with stem cell-like properties. These cells, often referred to either as “cancer stem cells” (CSCs) or as “tumor-initiating cells” (TICs), are responsible for forming the bulk of tumor. These CSCs possess both self-renewal and differentiation capabilities, and are believed to give rise to tumor heterogeneity. Furthermore, they have been shown to be associated with the most lethal characteristics of tumors—drug resistance and metastasis. The first evidence of the existence of CSCs came from studies of hematological malignancies in 1994. More recently, CSCs have been identified in a number of solid tumors, including breast, brain, skin, lung, colon, pancreatic, liver, head and neck, prostate, ovarian, and gastric cancers.
Osteosarcoma is the most common primary bone malignancy and accounts for 60% of all malignant childhood bone tumors. Before multi-agent chemotherapy, amputation provided a long-term survival rate of only ˜20%. Since the 1970s, combination chemotherapy along with limb-sparing surgery has been the main treatment for osteosarcoma. Currently, the 5-year survival for patients with osteosarcoma has been reported to be 50% to 80%. However, this survival rate has not improved over the last 10 years, and fully 40% of osteosarcoma patients die of their disease.
Targeting molecules important in tumorigenesis, known as “targeted therapy”, has been an exciting development in cancer treatment in the past ten years. However, no targeted therapy is currently available for osteosarcoma. Therefore, there is a great need for developing new osteosarcoma treatments.
CD133, also known as AC133 and Prominin 1 (PROM1), is a five-transmembrane glycoprotein of unknown function. It was the first identified member of the prominin family of five-transmembrane glycoproteins. In 1997, Yin et al. produced a novel monoclonal antibody that recognized the AC133 antigen, a glycosylation-dependent epitope of CD133, and they detected expression of AC133 in CD34-positive progenitor cells from adult blood. CD133 cDNA encodes a 5-transmembrane domain molecule with an extracellular N-terminus, a cytoplasmic C-terminus, and two large extracellular loops with eight consensus sites for N-linked glycosylation. A characteristic feature of CD133 is its rapid downregulation during cell differentiation. This feature makes CD133a unique cell surface marker for the identification and isolation of stem cells and progenitor cells in several tissues. According to the CSC theory, CSCs express some of the stem cell markers of normal stem cells. Therefore, tumor cells expressing CD133 independently or in combination with other stem cell or progenitor cell markers are thought to represent CSCs. To date, however, the molecular mechanisms underlying the phenotype of CSCs expressing CD133 cell surface marker have remained obscure.
MicroRNAs (miRNAs), first discovered in 1993 as a small non-protein-coding RNA, are small regulatory RNA molecules that modulate the expression of their target genes and play important roles in a variety of physiological and pathological processes, such as development, differentiation, cell proliferation, apoptosis, and stress responses. miRNA biogenesis requires several post-transcriptional processing steps to yield the functional mature miRNA. Over the past several years, many miRNAs have been investigated in various human cancers. The deregulation of the expression of miRNAs has been shown to contribute to cancer development through various kinds of mechanisms, including deletions, amplifications, or mutations involving miRNA loci, epigenetic silencing, the dysregulation of transcription factors that target specific miRNAs, or the inhibition of processing. miRNA expression profiling is of increasing importance as a useful diagnostic and prognostic tool, and many studies have indicated that miRNAs act either as oncogenes or as tumor suppressors.
The human miRNAs miR-1 and miR-133a are located on the same chromosomal region, in a so-called cluster. Enriched in muscle, they are miRNAs that inhibit proliferation of progenitor cells and promote myogenesis by targeting histone deacetylase 4 (HDAC4) and serum response factor (SRF), respectively. miR-1 has been reported to be overexpressed in individuals with coronary artery disease, while both of these miRNAs have been reported to be expressed at low levels in cardiac hypertrophy. Despite a number of studies, their importance in muscle physiology and disease still remains unclear. Recently, miR-133a (the name of which bears no relationship to the name CD133) has been considered to be dispensable for the normal development and function of skeletal muscle. However, the relationship between these miRNAs and CSCs has, until now, been unknown.
The human miRNA miR-10b has been found to be positively associated with high-grade malignancy. This association held true for various types of cancer. miR-10b is one of the most significantly upregulated miRNAs in human pancreatic adenocarcinomas and glioblastomas, two types of highly metastatic and/or invasive cancers. This miRNA is highly expressed in metastatic cancer cells propagated as cell lines, as well as in metastatic breast tumors from patients, and is also upregulated in metastatic hepatocellular carcinomas relative to those that are not metastatic. The importance of miR-10b in sarcoma development has not previously been reported.